The desirability of coating medical devices such as, inter alia, surgical implants, sutures and wound dressings with pharmaceutical agents is well documented in the art. Such coated devices could theoretically provide a means for locally delivering pharmaceutical or therapeutic agents at the site of medical intervention to treat a variety of diseases. For example, surgical implants or sutures coated with antibiotics can provide local delivery of antibiotic directly at an implantation or suture site, thereby decreasing the onset of infection following the surgical intervention.
Polymer compositions and methods for coating implants, especially sutures, are well-known in the art. Such coatings have been applied to surgical sutures to improve fiber lubricity, knot snug-down and tie-down performance, and for local delivery of pharmaceutical agents such as antibacterial agents. For example, there has been extensive application of the homopolymer poly(glycolic acid) (see for example U.S. Pat. No. 3,277,003) and copolymers of glycolic acid with a variety of other monomers which produce absorable polymer (see for example U.S. Pat. No. 3,839,297). Other polymers that have been used to coat sutures include U.S. Pat. No. 5,378,540 (polycaprolactones); U.S. Pat. No. 5,312,437 (poly(oxypropylene)glycol/lactide/glycolide copolymer); U.S. Pat. No. 5,147,383 (polyvinyl esters); U.S. Pat. No. 5,123,912 (poly(alkylene)glycol/lactide/glycolide copolymer); U.S. Pat. No. 5,102,420 (polyetheramide); U.S. Pat. No. 5,100,433 (p-dioxanone/.epsilon.-caprolactone copolymer); U.S. Pat. No. 5,032,638 (homopolymer of hydroxy butyrate linkages); U.S. Pat. No. 4,857,602 (triblock polymers of glycolide/poly(alkyleneoxide)/trimethylene carbonate); U.S. Pat. No. 4,844,067 (sucrose fatty esters); U.S. Pat. No. 4,711,241 (glycolic acids): U.S. Pat. No. 4,649,920 (poly(alkylene oxides)); U.S. Pat. No. 4,532,929 (fatty acids); and U.S. Pat. No. 4,433,688 (isocyanate capped polyhydroxylated polyesters).
It has been suggested that several of these biodegradable polymer coatings can theoretically be used to coat sutures and implants with pharmaceutical agents, with the biodegradable polymeric coating providing controlled release of the pharmaceutical agent at the site of surgical intervention. For example, U.S. Pat. No. 5,378,540 describes compositions for coating a surgical suture with a biodegradable polylactone polymeric sheath, optionally containing a pharmaceutical agent. The suture is coated by dipping it in an organic solvent containing the polymer and pharmaceutical agent and allowing the suture to dry.
However, prior art methods for coating sutures and implants have typically been limited with respect to the types of pharmaceutical agents that can be incorporated into the coating sheath. Generally, the pharmaceutical agents must be hydrophobic, as they must be soluble in the organic solvent used to dissolve the polymer prior to coating the suture.
While methods have been developed to coat implants with water soluble pharmaceutical agents, especially anti-bacterial agents, these methods are not readily adaptable to easily and efficiently coat medical devices with a wide variety of pharmaceutical agents, especially nucleic acids, as they either require complex, expensive machinery or suffer from other undesirable limitations. These methods are also not suitable for providing coatings exhibiting controlled or sustained release of pharmaceutical agents.
For example, U.S. Pat. No. 5,474,797 describes a process for dry-coating implants with bactericidal agents involving depositing a 0.5-10 .mu.m thick layer of bactericidal agent onto the implant in the form of ionized atoms via ion-beam-assisted deposition in a vacuum chamber. In addition to requiring expensive equipment, this method also suffers from the limitation that the pharmaceutical agent to be administered must be readily ionizable. Furthermore, the coated implants do not provide controlled or sustained release of bactericidal agent.
U.S. Pat. No. 4,952,419 describes a method for coating implants with bactericidal agents that involves applying a film of silicone oil to the implant surface followed by contacting the oiled surface with powdered antibacterial agents. While relatively simple, this method requires several manipulations and does not allow for sustained delivery of bactericidal agents. The method also requires that the pharmaceutical agent be available in powdered form.
U.S. Pat. No. 4,024,871 describes sutures impregnated with water soluble antimicrobial agents. The sutures are impregnated by soaking in a dilute solution of antimicrobial agent. The sutures are dried, leaving a residue of antimicrobial agent distributed substantially throughout the suture filament. The suture is then top-coated with polyurethane to prevent the antimicrobial agent from leeching out of the suture. As is readily apparent, this method is not suitable for coating devices that do not readily take up, or become impregnated with, the desired pharmaceutical agent. Furthermore, because the suture is top-coated with polyurethane, this method is not useful for the controlled delivery of pharmaceutical agents at the site of surgical intervention. Rather, the suture is impregnated with an antimicrobial agent to insure its sterility.
Accordingly, there remains a need in the art for compositions and methods which allow medical devices to be easily and efficiently coated with a wide variety of pharmaceutical agents, especially hydrophilic pharmaceutical agents, and that further provide controlled or sustained release of the pharmaceutical agents into the local area surrounding the site of medical intervention.
The prior art methods for coating implants and sutures also typically deposit a sheath or layer of polymer, optionally containing a pharmaceutical agent, tens of microns thick onto the implant or suture. As the biodegradable polymeric coating dissolves, the pharmaceutical agent is released into the area surrounding the implant, where it may be taken up by the surrounding cells. Thus, implants and sutures coated with the prior art compositions and methods deliver pharmaceutical agents extracellularly.
Often times, it is desirable to deliver pharmaceutical agents intracellularly rather than, or in addition to, extracellularly. Such applications are useful where, for example, the pharmaceutical agent cannot easily penetrate or traverse the cellular membrane. Examples of such pharmaceutical agents include oligonucleotides such as antisense DNA and RNA, ribozymes, DNA for gene therapy, transcription factors, growth factor binding proteins, signalling receptors and the like.
Microspheres and/or nanospheres are a widely used vehicle for delivering drugs intracellularly. Generally, microspheres and/or nanospheres comprise a biodegradable polymeric core having a pharmaceutical agent incorporated therein. Microspheres are typically spherical and have an average diameter of about 1 to 900 .mu.m. Nanospheres are typically spherical and have an average diameter of less than 1 .mu.m, usually less than about 300 nm.
Advantages of microsphere and/or nanosphere pharmaceutical formulations include their ability to enter cells and penetrate intracellular junctions. Another advantage of microspheres and/or nanospheres is their ability to provide sustained or controlled release of pharmaceutical agents. Thus, microspheres and/or nanospheres provide a means for intracellular as well as extracellular controlled or sustained delivery of pharmaceutical agents.
Accordingly, it would be extremely advantageous to have available methods and compositions for coating medical devices with microspheres and/or nanospheres containing pharmaceutical agents. Such coated devices would facilitate intracellular as well as extracellular local controlled or sustained release of pharmaceutical agents at the site of medical intervention. These devices would be particularly advantageous for delivering drugs that do not readily penetrate or traverse cellular membranes.
Gene therapy is generally understood to refer to techniques designed to deliver nucleic acids, including antisense DNA and RNA, ribozymes, viral fragments and functionally active therapeutic genes into targeted cells (Culver, 1994, Gene Therapy: A Handbook for Physicians, Mary Ann Liebert, Inc., New York, N.Y.). Such nucleic acids may themselves be therapeutic, as for example antisense DNAs that inhibit mRNA translation, or may encode therapeutic proteins that promote, block or replace cellular functions.
Perhaps one of the greatest problems associated with current gene therapy strategies, whether ex vivo or in vivo, is the inability to transfer nucleic acids efficiently into a targeted cell population and to achieve a high level of expression of the gene product in vivo. Viral vectors are regarded as the most efficient system, and recombinant replication-defective viral vectors have been used to transduce (i.e., infect) cells both ex vivo and in vivo. Such vectors have included retroviral, adenovirus, adeno-associated viral vectors and herpes viral vectors. While highly efficient at gene transfer, the major disadvantages associated with the use of viral vectors include the inability of many viral vectors to infect non-dividing cells; problems associated with insertional mutagenesis; problems associated with the ability to "turn on" gene expression over time in the few cells that are transfected; potential helper virus production and/or production and transmission of harmful virus to other human patients.
In addition to the low efficiency of most cell types to uptake and expression of foreign nucleic acids, many targeted cell populations are found in such low numbers in the body that the efficiency of transformation of these specific cell types is even further diminished. Therefore, any gene therapy method which increases the efficiency with which nucleic acids are transferred into targeted cells would greatly enhance the overall usefulness of gene therapy protocols.
Recently, it has been discovered that proliferating repair cells active in the wound healing process are surprisingly efficient at taking up and expressing nucleic acids (copending application Ser. No. 08/631,334, filed Apr. 8, 1996 now U.S. Pat. No. 5,962,427). These proliferating repair cells could provide an efficient means for administering gene therapy directly at a surgical or implantation site. It would therefore be extremely advantageous to have available methods and compositions for coating medical devices with a polymeric matrix containing nucleic acids. Such coated devices would provide a convenient means for efficiently transferring therapeutic nucleic acids to proliferating repair cells directly at a wound or site of surgical intervention. The proliferating repair cells would then act as local "bioreactors" for production of therapeutic gene products, such as therapeutic proteins. Of particular significance would be the availability of nucleic acid-coated sutures, as sutures de facto will always be surrounded by injured tissue.
In some circumstances, it may be advantageous for the devices to be coated with microspheres and/or nanosphere containing nucleic acids, as described above. However, transfer of nucleic acids into wounded tissue need not be mediated via microspheres and/or nanospheres.
The difficulty of wound healing and tissue regeneration following surgical intervention is also well documented in the art. In addition, it is well-known that many fragile tissue types, such as normal and diseased liver tissue, tissues in patients suffering from certain metabolic disorders such as diabetes, and tissues that have been irradiated such as tissues following cancer surgery, have difficulty holding sutures.
Currently available wound healing therapies involve the administration of therapeutic proteins. Such therapeutic proteins may include regulatory factors involved in the normal healing process such as systemic hormones, cytokines, growth factors and other proteins that regulate proliferation and differentiation of cells. Growth factors, cytokines and hormones reported to have such wound healing capacity include, for example, the transforming growth factor-.beta. superfamily (TGF-.beta.) of proteins (Cox, D. A., 1995, Cell Biology International 19:357-371); acidic fibroblast growth factor (FGF) (Slavin, J., 1995, Cell Biology International 19:431-444); macrophage-colony stimulating factor (M-CSF); and calcium regulatory agents such as parathyroid hormone (PTH).
A number of problems are associated with the use of therapeutic proteins in wound healing therapies. For example, the purification and/or recombinant production of therapeutic proteins is often an expensive and time-consuming process. Once purified, most protein preparations are unstable making storage and use cumbersome.
Additionally, because of the short half-life in the body due to proteolytic degradation, repeated administration of high doses of protein are required to ensure that sufficient amounts of the protein reach the tissue.
Finally, for a variety of proteins such as membrane receptors, biological activity is dependant on correct expression and localization in the cell. For many proteins, correct cellular localization occurs as the protein is post-translationally modified. Therefore, such proteins cannot be administered in such a way as to be taken up and properly localized inside the cell.
It would therefore be particularly advantageous to have available medical devices, especially surgical sutures, coated with nucleic acids that stimulate wound healing. Such coated devices would provide for the controlled or sustained release of the nucleic acids into a wound or site of surgical intervention. As described above, proliferating repair cells will take up and express the nucleic acids, thereby stimulating local wound healing.
The coated devices would be particularly useful for difficult surgical situations where compromised wound healing may be a problem, such as surgery in patients having diabetes. Coated sutures would not only enable mechanical juxtaposition of tissues, but through repair cell-mediated nucleic acid transfer would stimulate wound healing along the suture line as well. Illustratively, such sutures would essentially "spot weld" the tissue together. Such sutures would also be useful for re-establishing normal functional tissue architecture at the suture line and in nearby regions.
Nucleic acid-mediated wound healing strategies overcome many of the shortcomings of current wound healing strategies. Unlike proteins, nucleic acids, particularly DNA, are extremely stable for prolonged periods of time under a variety of storage conditions. In addition, since the transfected cells act as bioreactors to produce encoded proteins, administration of even small amounts of nucleic acids would provide therapeutic benefit. Furthermore, since the encoded proteins are expressed in the mammalian cell, they may be post-translationally modified and/or spliced to yield active protein.
As is readily apparent from the above discussion, presently there are no methods and/or compositions available which allow medical devices to be easily and efficiently coated with a wide variety of pharmaceutical agents, especially water-soluble or hydrophilic pharmaceutical agents, that permit local controlled or sustained release of such agents at a site of medical intervention for the treatment of wounds or disease.
There are also presently no methods or compositions available for coating medical devices with microsphere and/or nanosphere pharmaceutical formulations that permit easy and efficient intracellular as well as extracellular local delivery of pharmaceutical agents that do not readily traverse or penetrate cell membranes for the treatment of wounds or disease.
Furthermore, there are currently no compositions or methods available for coating medical devices with nucleic acids, especially nucleic acids that stimulate wound healing, that permit easy and efficient targeted local delivery of nucleic acids in vivo.
Accordingly, these and other deficiencies in the art are objects of the present invention.